High friction surfacing (HFS) is an anti-skid road surfacing system installed in areas where the risk of a vehicle skidding accident is high. Examples would be approaches to traffic lights, pedestrian crossings and roundabouts, as well as on steep inclines and dangerous bends. Research has shown that the number of accidents/fatalities can be substantially reduced when HFS systems are installed at high risk locations.
HFS systems comprise of a resin that is applied to an existing road surface substrate. The resin holds and binds a special aggregate comprising calcined bauxite, providing a high performance anti-skid surface. After the HFS system has cured it is opened to traffic.
There are two main categories of HFS, namely Cold Applied and Hot Applied. The cold applied system incorporates a resin binder which is adhered to the road surface substrate. Calcined bauxite aggregates are then broadcast over the resin binder coating. For the hot applied system, the calcined bauxite aggregate and resin binder are pre-mixed together. During installation the pre-mixed material is heated up and mixed in a truck mounted boiler at high temperatures. The material is then screeded over the road surface substrate.
The finished HFS system gives superior performance over other highway materials in terms of skidding resistance (i.e. grip) and as a result increases road safety to the road user at high risk locations.
HFS systems are governed in the UK by the Highway Authorities Product Approval Scheme (HAPAS). HAPAS was set up in 1995 to establish a nationally recognized approval scheme for innovative products and systems used in highway works. The British Board of Agrément (BBA) is the authority which has responsibility for governing the HAPAS scheme. The BBA give guidance for the assessment and certification of HFS systems and for the assessment and surveillance for HFS installers.
The aggregate specified for use in HFS systems is typically 100% calcined bauxite. Calcined bauxite has unique properties which gives it excellent performance in terms of skidding and wear resistance. However, this material is available in very few locations throughout the world. Geologically, it is not available in the UK or Ireland and the two main sources are China and Guyana in South America. As a result, calcined bauxite is very expensive and has a negative impact on the environment having to be shipped half way around the world to get to its desired location.